The present invention relates to a pressure-resistant helical corrugated pipe adapted to be buried in the ground, so that telecommunication cables such as an electric cable and a telephone cable can be installed in such a corrugated pipe for the purpose of protecting such cables. Also, such a corrugated pipe is used as a water main pipe, a sewer pipe, or a liquid transport pipe used in a plant or a factory.
Among such conventional pressure-resistant helical corrugated pipes, the type of corrugated pipes adapted for underground use have been required to be pressure-resistant in order to withstand a great ground pressure. In a conventional underground pressure-resistant pipe as shown in FIGS. 10 and 11 (see, for example, Japanese Laid-Open Utility Model Application No. 141889/86 filed by the Applicant of the present application), a continuous reinforcing belt plate 06 made of a thin metal plate is embedded in a pipe wall 01 and extends over a top portion 02 of the helical corrugation, opposite side wall portions 03 and 04, extending from the top portion 02, and part of a bottom portion 05.
However, in such a helical corrugated pipe, the reinforcing metal belt plate 06, which is embedded in the top portion 02 of the pipe wall 01, the opposite side wall portions 03 and 04 and the bottom portion 05, is a continuous unitary plate, and therefore it is not possible to thicken only the top portion 02 of the pipe wall 01 which most contributes to the pressure-resistant strength to withstand a flattening force. As a result, the whole of the metal belt plate 06 must be thickened. When such a thickened metal belt plate 06 is used, the shaping and processing is not easy, and also it is not easy to impart a helical corrugated shape to the metal belt plate when it is helically wound, and as a result the metal belt plate is liable to deformation due to strain. This results in a problem that it is difficult to manufacture the helical corrugated pipe having a good appearance.